There are in the art a number of flexible guide wires used in medical applications such as introducing catheters into human cardiovascular systems. Exemplary such devices are shown in U.S. Pat. Nos. 3,789,841, 4,538,622 and 4,545,390, which are hereby incorporated by reference. As discussed in these prior patents, in one typical application, such guide wires are introduced into a patient's femoral or brachial artery and are advanced through the artery into the coronary region, and the guide wire is manipulated to steer the device selectively into deeper and smaller coronary arteries. These prior art devices have a number of limitations. The wires tend to "set" when curved into the tortuous configuration required to follow along the artery and, particularly when curved, will not transmit torque/rotation from end-to-end on a substantially one-to-one basis.
The art also teaches a number of flexible power transmission shafts and couplings. See, e.g., U.S. Pat. Nos. 177,490, 779,374, 1,481,078, 1,678,335, 2,573,361, 3,628,352, 4,112,708, and U.S. Pat. No. Re. 25,543. These devices are, because among other things of their size, not useful in medical cardiovascular devices. Moreover, their design and construction is typically such that substantially one-to-one rotational torque transmission is neither necessary nor desired. In the flexible coupling of U.S. Pat. No. Re. 25,543, the circumference and inner surfaces of the individual springs are either ground to size or otherwise calibrated in order to telescope the individual layers into each other with a tight fit.